Aiming at problem of the inspection robot for the high voltage power transmission line with a small working space that caused the robots could not cross drainage line efficiently, a new type of inspection robot with three manipulate arms is proposed. The front and rear arm of the robot was designed of a parallel quadrilateral structure, with a local closed-chain mechanism, was not entirely open-chain structure but mixed. So a new approach for constructing the kinematic equation for the robot arm was also presented based of analysis of the characteristics of local closed chain mechanism. Using MATLAB software to analyze the robot arm’s operating space for crossing obstacles, and the process of the robot crossing the drainage line and walking on the lines was simulated through Adams software verifying the rationality of the robot arm’s structure. The inspection robot with three arms which adopt local closed-chain can cross various obstacles on the line more stably and reliably.